Variations on the slotted-tube resonator: Rectangular and elliptical coils

Two designs (one rectangular, one elliptical) are proposed as efficient alternatives to noncylindrical birdcage RF coils. These designs are based on the slotted-tube resonator and their performance relies on the natural current distribution in the conductors due to the eddy current effects at high frequencies. A Finite element method program, solving the full set of Maxwell's equations, has been employed to accurately characterize and optimize the field homogeneity of the proposed noncylindrical coils. The optimum configuration of each design is presented, taking into account the effect of the RF shield. The proposed designs are compared to several configurations presented in the literature. Two coils (one rectangular, one elliptical) have been constructed and tested in a 0.6 T imaging system, A rectangular coil has been built to operate at 300 MHz, MR images substantiate the usefulness of these coils. (C) 1999 Elsevier Science Inc.